Local residents attend a Gwinnett County open house and information session on its proposed transit plan at the Gwinnett Justice and Administrative Center on April 25 in Lawrenceville. CURTIS COMPTON / CCOMPTON@AJC.COM

When, exactly, they need to decide if they want to add such a referendum to November’s ballot has been the subject of plenty of confusion. But Commission Chairman Charlotte Nash said the facts are pretty straightforward.

Under the new legislation, she said, such a referendum is to be treated like any other special election — meaning that Gwinnett could technically wait until 30 days before the Nov. 6 election to add it to the ballot.

“If you back it up for practical considerations, like finalization of the ballot and getting it ready and that kind of stuff, I think it probably needs to be done by the end of August,” Nash said.

Nash said her assessment has been confirmed by a handful of attorneys.

House Bill 930, authored by Rep. Kevin Tanner (R-Dawsonville) and signed into law last month by Gov. Nathan Deal, created a regional transit agency called The ATL and authorized 13 suburban counties to hold referendums asking voters if they want to opt-in on a 30-year, transit-funding sales taxes.

“The ATL” won’t be formed until Jan. 1, 2019, but Gwinnett-specific language in the bill would allow the county to go ahead and hold a referendum this fall. If a vote is held this fall, it would have to be about joining the existing MARTA system, which will be under the guidance of The ATL once its formally created.

County leaders said it will all probably come down to money.

Information distributed last week by an environmental group called Georgia Conservation Voters asserted that Gwinnett would have to authorize a MARTA contract at least 120 days before November’s election. But Nash said HB 930 removed that requirement from the MARTA Act.

She said Gwinnett commissioners could vote on a new MARTA contract during the same meeting they voted to call a referendum.

The first step toward holding a possible referendum would be for the commission to approve the county’s new transit development plan.

As presented to the public in recent months, the plan calls for extending MARTA’s heavy rail line about four miles from the existing Doraville station and into Gwinnett County. A “multimodal hub” would be built somewhere in the vicinity of Jimmy Carter Boulevard and I-85.

The plan also suggests building multiple bus rapid transit lines and greatly expanding local bus service.

Gwinnett Department of Transportation Director Alan Chapman said the final draft of the plan is “pretty similar” to what has been previously presented. It’s scheduled to be presented Tuesday to the Board of Commissioners, which would likely vote on its formal adoption sometime in July.

That would leave plenty of time for the county to call a transit referendum — if that’s what officials ultimately decide to do.

“We are still assessing our options, and part of it, as I’ve said before, is giving the district commissioners a chance to get their minds wrapped around the changes that came as a result of House Bill 930 and what they think is the best way to approach it,” Nash said.